The present invention relates to an optical module for use in a subcarrier multiplexed (SCM) optical transmission system and capable of reducing the distortion of a signal light due to multiple reflections.
An SCM optical transmission system transits a signal light modulated by frequency-multiplexed carriers and can send multichannel video signals and radio signals at low cost. This kind of system is, therefore, a promising application to the trunk lines of cable television (CATV) systems, mobile radio communication systems, etc. The prerequisite with such an application is that distortions due to the interference between individual carriers, e.g., intermodulation distortion, higher harmonic distortion and mixed modulation distortion be strictly suppressed.
In the SCM transmission system, when multiple reflections occur, the transmitted signal involves distortions attributable to the interference between a signal light and a multiple reflected light. Distortions due to multiple reflections are discussed in, for example, W. Domon et al "Distortion due to Optical Reflection and Dispersion in Optical Fiber Feeder System", the Institute of Electronics, Information and Communication Engineers of Japan, Technical Report, OCS 91-79.
A laser diode, photodiode or similar optical device for use in the SCM transmission system is usually arranged in an optical module. The optical module is often connected to an optical fiber transmission part by an optical connector. In this condition, it is likely that the signal suffers from distortions due to multiple reflections between the reflection point of the transmission path and the module or multiple reflections between the module and the optical connector.